The invention relates to a process and agent for testing the sensitivity of bacteria towards antibiotics with a primary action in murein biosynthesis.
Before antibiotic therapy, the sensitivity of the pathogen towards various antibiotics should, where possible, be determined. The test methods used today for testing the sensitivity are mostly based on detection of the inhibition of growth of pure cultures of the microorganism in the presence of the antibiotic.
In an in vitro sensitivity test, the antibiotic action depends on many factors, for example on the growth phase of the microorganisms, the nutrient medium and the polulation density. Standard methods for testing the sensitivity of microorganisms towards antibiotics are the dilution test in agar or a broth and the agar diffusion test.
The tests are in practice evaluated by visual examination of the test batches with respect to microorganism growth, for example after 24 hours incubation, by determination of the turbidity in the dilution series test or of the inhbiting areola diameter in the agar diffusion test. The analysis times in the dilution series test can usually be shortened to 4-8 hours by modern sensitive analytical methods, such as impedance measurement or laser nephelometry. However, the corresponding analytical instruments are as a rule expensive, so that their use is only justified in laboratories with a large number of samples; with average analytical times of 4-8 hours, the result is frequtently available only after office hours, so that the advantage of the shortened analytical time is cancelled out again by the delayed forwarding of information.
In practice, there is therefore an urgent need for a sensitivity test which gives results very rapidly and can also be carried out in smaller laboratories without too great an expenditure on apparatus. Rapid tests to ascertain the sensitivity of microorganisms towards chemotherapeutics makes more controlled use of the antibiotics possible, which leads, for example, to a shortening in the treatment time for the patient and to a check in the selectioning of multi-resistant bacterial strains.
The antibiotics whose primary site of action is murein biosynthesis include, for example, cycloserine, vancomycin and bacitracin, in addition to the penicillins and cephalosporins, which are very useful in therapy. Penicillins and cephalosporins are characterized chemically by the presence of a .beta.-lactam ring. The resistance properties of Gram-negative bacteria towards .beta.-lactam antibiotics is different from that of Gram-positive organisms. Most of the Gram-positive bacteria produce relatively large amounts of extracellular .beta.-lactamases which split the .beta.-lactam ring and can thus inactivate the .beta.-lactam antibiotics. For the sensitivity of Gram-negative bacteria towards .beta.-lactam antibiotics, a penetration resistance is frequently of substantially greater importance than a resistance caused by .beta.-lactamases. The cell-linked .beta.-lactamases from Gram-negative bacteria are formed in substantially lower concentrations than the extracellular .beta.-lactamases from Gram-positive bacteria. In the case of Gram-negative bacteria, there is frequently no correlation between the minimum inhibitory concentration of the .beta.-lactam antibiotics and the .beta.-lactamase activity. .beta.-Lactamase-positive bacteria are to be found among both the .beta.-lactam antibioticsensitive and the .beta.-lactam antibiotic-insensitive Gram-negative bacteria. The known rapid .beta.-lactamase tests thus are of no significance by themselves for testing the sensitivity of, for example, Enterobacterianceae towards .beta.-lactam antibiotics.